As a light source used for a vehicle headlamp, a conventional incandescent lamp is replaced by a discharge lamp (HID lamp), and further superseded by a light emitting diode (LED) in recent years. However, all the light sources should be cooled since they generate heat as there are somewhat differences in the amount of generated heat. On the other hand, snow often deposits on the front lens of the vehicle headlamp during snowfall particularly in cold districts, and thus it is required to heat up the front lens so as to melt the snow thereon.
As one technology for cooling a vehicle headlamp, a technology for radiating the heat by extending a heat radiating section of a vehicle headlamp forwardly from the light source thereof is known. For example, Patent Document 1 discloses a projector-type vehicle headlight unit where optical positional relations between components can be adjusted with a high degree of accuracy, the number of components can also be reduced, and further an excellent effect of heat dissipation can be achieved. The projector-type vehicle headlight unit has a structure where a member for fixing an LED and radiating the heat thereof and a member for securing a convex lens are provided integral with each other. According to the arrangement of the headlight unit, the convex lens, the light source, and the heat radiating member thereof are provided integral with each other. Thus, adjustment of the optical axis of the headlamp is facilitated, and a heat sink (heat radiating member) extending to the convex lens section can transfer heat to the vicinity of the convex lens to dissipate the heat therefrom.
Further, a technology for radiating the heat generated by a light source (LED) with a heat pipe is known as another technology for cooling a vehicle headlamp. For example, Patent Document 2 discloses a vehicle lamp where a measure against the heat from an LED is compatible with the enhancement of degree of freedom on the position of the LED to be disposed. The vehicle lamp disclosed by Patent Document 2 has a structure where a general heat pipe is disposed with a heat adsorbing section connected to the LED being arranged below and with a heat radiating section being arranged above, such that an effective performance based on the mechanism of heat conduction is obtained.
Furthermore, Patent Document 3 discloses a vehicle lamp where the technology disclosed in Patent Document 2 is improved by looping a rod-shaped heat pipe. In the vehicle lamp disclosed in Patent Document 3, the lamp is arranged such that the flow of liquid and vapor present within the heat pipe is not interrupted even when a vehicle having the headlamp mounted thereon inclines.
Meanwhile, Patent Document 4 discloses a technology for restricting the temperature rise of semiconductor light emission elements in a vehicle headlight arranged such that light distribution patterns of two or more types are formed by a plurality of lamp units using a semiconductor light emission element as a light source. In the technology disclosed in Patent Document 4, the heat generated by the LEDs is transferred to a front lens disposed lower than the LEDs by using a heat pipe.
In addition, Patent Document 5 discloses a vehicle lamp where the temperature of LEDs can be more positively reduced. In the vehicle lamp, the heat generated by the LEDs is transferred to the upper portion of the case of a headlamp disposed higher than the LEDs and to a front lens disposed lower than the LEDs by using a heat pipe.
Lastly, Patent Document 6 discloses a vehicle lamp that can promptly remove the fogging of a front lens and ice and snow deposited thereon as one technology for warming the front lens of a vehicle headlamp. In the vehicle lamp, a semiconductor light emission element is used as a light source, one side of a heat-conduction board is connected with the vicinity of a heat sink where the semiconductor light emission element is disposed, and the other side of the heat-conduction board is in contact with a portion of the front lens which does not get involved in the formation of a light distribution. In this way, the occurrence of fogging and the deposition of snow and ice can be prevented and further maintenance can be simplified by using the heat generated during lighting of the semiconductor light emission element.
Patent Document 1: JP-A-2006-114275
Patent Document 2: JP-A-2004-127782
Patent Document 3: JP-A-2006-164967
Patent Document 4: JP-A-2004-311224
Patent Document 5: JP-A-2006-286395
Patent Document 6: JP-A-2007-273369
However, the above-described conventional technologies each have the following problems. To be more exact, in the technology disclosed by Patent Document 1, the heat is transferred to the vicinity of the convex lens by the heat sink (heat radiating member) extending to the convex lens section; however, the heat conduction performance of the heat sink is mainly dependent on the heat or thermal conductivity of the metal material forming the heat sink, the preparation is necessary, of a large-sized member in order to secure a sufficient thermal conduction quantity, a cost increase cannot be avoided, and moreover, the use of a large-sized member is undesirable from the viewpoint of space. Furthermore, the technology does not consider the heat radiation at portions located forward of the convex lens.
Further, in the technology disclosed in Patent Document 2, the LED and a case are connected to each other with a rigid heat pipe, and thus the optical axis cannot be adjusted. Moreover, in the technology disclosed by Patent Document 3, the heat pipe is fixed movably to the LED (heat receiving section), and thus the optical axis can be adjusted though the heat conduction performance thereof at the fixed portion is poor. However, in the technologies disclosed by Patent Document 2 and Patent Document 3 discussed above, the heat generated by the LED is discharged outwardly from the case of the headlamp, and thus it is impossible to warm the front lens of the headlamp. Incidentally, in the technology disclosed by Patent Document 3, the loop-shaped heat pipe is arranged such that the heat conduction performance thereof can be obtained even when the liquid and the vapor present internally therein circulate from whichever side of the loop, and thus it is impossible to transmit the heat in one direction toward a specific portion by the circulation of the liquid and the vapor located therein.
Moreover, in the technology disclosed by Patent Document 4, the heat pipe is fixed to the heat conduction member of the LEDs, and thus the heat conduction performance to the heat pipe is excellent. However, the arrangement for disposing components is complicated. Besides, in the technology disclosed by Patent Document 5, the heat pipe is in contact with the heat conduction member of the LEDs; however, the heat pipe is not secured to the member. Thus, the system has to admit that the performance for conducting the heat to the heat pipe is deteriorated. According to each of the technologies disclosed by Patent Document 4 and Patent Document 5 discussed above, an arrangement for radiating the heat downwardly from the heat adsorbing section with a heat pipe is employed, and thus the heat conduction mechanism of the heat pipe is not efficiently used. Therefore, the heat pipe does not fully produce an effect in its heat conduction performance, the heat generated by the LED is not sufficiently adsorbed, resulting in insufficient warming of the front lens of necessity.
Furthermore, according to the technology disclosed by Patent Document 6, the heat-conduction board for connecting the vicinity of the heat sink where the semiconductor light emission element is disposed with the portion of the front lens which does not get involved in forming the light distribution is formed of a metallic plate such as copper or aluminum plate. Thus, just as with Patent Document 1 discussed above, the heat conduction performance thereof depends mainly on the heat conductivity of the metal material. Therefore, there is a problem that it is necessary to prepare a large-sized member in order to secure a sufficient heat conduction quantity, an increase in cost is unavoidable, and moreover, the use of a large-sized member is undesirable from the viewpoint of space
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a vehicle headlamp capable of cooling a light source and also efficiently warming a front lens.